1. Technical Field
The present disclosure relates to an optical waveguide and a method of manufacturing the same and a method of manufacturing an optical/electrical hybrid substrate and, more particularly, to an optical waveguide for transmitting a light signal between a light emitting element and a light receiving element, and a method of manufacturing the same, and a method of manufacturing an optical/electrical hybrid substrate.
2. Related Art
In recent years, with the speed-up of an information communication, a light is employed instead of an electric signal as the medium of the information communication. In such optical communication field, the conversion from a light signal to an electric signal and the conversion from the electric signal to the light signal are required, and also various processes such as the optical modulation, etc. in the optical communication are required. Therefore, the development of the optical/electrical hybrid substrate for handling the above converting processes is proceeding.
FIG. 1 is a sectional view showing an optical/electrical hybrid substrate in the related art.
As shown in FIG. 1, an optical/electrical hybrid substrate in the related art includes a wiring substrate 201, an optical waveguide 202, a light emitting element 203, a light receiving element 204, and underfill resins 206, 207.
The wiring substrate 201 has a substrate main body 211, through vias 212 and 213, upper wirings 215, 216, 223 and 224, insulating layers 218 and 231, vias 221, 222, 233 and 234, solder resists 226 and 239, and lower wirings 228, 229, 236 and 237.
The substrate main body 211 is a core substrate shaped like a plate. The through vias 212, 213 are provided to pass through the substrate main body 211. An upper end portion of the through vias 212 is connected to the upper wiring 215, and a lower end portion is connected electrically to the lower wiring 228. An upper end portion of the through vias 213 is connected to the upper wiring 216, and a lower end portion is connected electrically to the lower wiring 229.
The upper wirings 215, 216 are provided on an upper surface 211A of the substrate main body 211. The insulating layer 218 is provided on the upper surface 211A of the substrate main body 211 to cover the upper wirings 215, 216. The via 221 is provided to pass through the insulating layer 218 arranged on the upper wiring 215. A lower end portion of the via 221 is connected to the upper wiring 215. The via 222 is provided to pass through the insulating layer 218 arranged on the upper wiring 216. A lower end portion of the via 222 is connected to the upper wiring 216.
The upper wiring 223 is provided on a portion of the insulating layer 218 corresponding to a forming position of the via 221. The upper wiring 223 is connected to an upper end portion of the via 221. The upper wiring 223 has a pad portion 241 connected electrically to the light emitting element 203. The upper wiring 224 is provided on a portion of the insulating layer 218 corresponding to a forming position of the via 222. The upper wiring 224 is connected to an upper end portion of the via 222. The upper wiring 224 has a pad portion 242 connected electrically to the light receiving element 204.
The solder resist 226 has opening portions that expose the pad portions 241, 242. The solder resist 226 is provided on the insulating layer 218 to cover portions of the upper wirings 223, 224 except the pad portions 241, 242.
The lower wirings 228, 229 are provided on a lower surface 211B of the substrate main body 211. The insulating layer 231 is provided on the lower surface 211B of the substrate main body 211 to cover the lower wirings 228, 229. The via 233 is provided to pass through the insulating layer 231 arranged under the lower wiring 228. An upper end portion of the via 233 is connected to the lower wiring 228. The via 234 is provided to pass through the insulating layer 231 arranged under the lower wiring 229. An upper end portion of the via 234 is connected to the lower wiring 229.
The lower wiring 236 is provided on a lower surface of a portion of the insulating layer 231 corresponding to a forming position of the via 233. The lower wiring 236 is connected to a lower end portion of the via 233. The lower wiring 236 has an external connection pad portion 245. The lower wiring 237 is provided on a lower surface of a portion of the insulating layer 231 corresponding to a forming position of the via 234. The lower wiring 237 is connected to a lower end portion of the via 234. The lower wiring 237 has an external connection pad portion 246.
The solder resist 239 has opening portions that expose the external connection pad portions 245 and 246. The solder resist 239 is provided on the insulating layer 231 to cover portions of the lower wirings 236, 237 except the external connection pad portions 245, 246.
The optical waveguide 202 is bonded to the solder resist 226 with an adhesive agent. The optical waveguide 202 includes: an optical waveguide main body 251 constructed by stacking a cladding layer 255, a core portion 256 and a cladding layer 257; a mirror 253 provided on an inclined surface 251A of the optical waveguide main body 251; and a mirror 254 provided on an inclined surface 251B of the optical waveguide main body 251.
FIG. 2 is a sectional view showing a portion, to which the light emitting element shown in FIG. 1 is connected, of the optical/electrical hybrid substrate in an enlarged manner.
By reference to FIG. 1 and FIG. 2, the light emitting element 203 has a terminal 261 and a light emitting portion 262 for emitting a light signal. The terminal 261 is fixed to the pad portion 241 by a solder 264. The light emitting portion 262 is arranged over the mirror 253 to oppose to the mirror 253 provided to the core portion 256. A light signal emitted from the light emitting portion 262 is reflected to the core portion 256 by the mirror 253.
As the characteristics of an optical/electrical hybrid substrate 200, it is important that a transmission loss of the light signal between the light emitting element 203 and the optical waveguide 202 should be small. In order to reduce a transmission loss of the light signal between the light emitting element 203 and the optical waveguide 202, it is important that a distance R1 from a center position S1 (a center position on an optical axis) of the mirror 253 provided to the core portion 256 to a center position of the pad portion 241 should be set to a predetermined distance RA and also a distance N1 from the light emitting portion 262 to the center position S1 (the center position the optical axis) of the mirror 253 provided to the core portion 256 should be set to a given distance NA.
FIG. 3 is a sectional view showing a portion, to which the light receiving element shown in FIG. 1 is connected, of the optical/electrical hybrid substrate in an enlarged manner.
By reference to FIG. 1 and FIG. 3, the light receiving element 204 has a terminal 266 and a light receiving portion 267 for receiving the light signal. The terminal 266 is fixed onto the pad portion 242 by the solder 264. The light receiving portion 267 is arranged over the mirror 254 to oppose to the mirror 254 provided to the core portion 256. The light receiving portion 267 is provided to receive the light signal reflected by the mirror 254.
As the characteristics of the optical/electrical hybrid substrate 200, it is important that a transmission loss of the light signal between the light receiving element 204 and the optical waveguide 202 should be small. In order to reduce a transmission loss of the light signal between the light receiving element 204 and the optical waveguide 202, it is important that a distance R2 from a center position S2 (a center position on an optical axis) of the mirror 254 provided to the core portion 256 to a center position of the pad portion 242 should be set to a given distance RB and also a distance N2 from the light receiving portion 267 to the center position S2 (the center position on the optical axis) of the mirror 254 provided to the core portion 256 should be set to a given distance NB.
The underfill resin 206 is a translucent resin capable of transmitting the light signal, and is provided to fill a clearance between the light emitting element 203 and the wiring substrate 201 and the optical waveguide 202. The underfill resin 207 is a translucent resin capable of transmitting the light signal, and is provided to fill a clearance between the light receiving element 204 and the wiring substrate 201 and the optical waveguide 202.
FIG. 4 to FIG. 7 are views showing steps of manufacturing the optical/electrical hybrid substrate in the related art. In FIG. 4 to FIG. 7, the same reference symbols are affixed to the same constituent portions as those of the optical/electrical hybrid substrate 200 in the related art.
By reference to FIG. 4 to FIG. 7, a method of manufacturing the optical/electrical hybrid substrate 200 in the related art will be described hereunder. At first, in steps shown in FIG. 4, the wiring substrate 201 is formed by the well-known approach.
Then, in steps shown in FIG. 5, the optical waveguide 202 is formed by the well-known approach. Concretely, the cladding layer 257, the core portion 256, and the cladding layer 255 are stacked sequentially on a supporting substrate (concretely, a substrate made of a resin). Then, both end portions of the structure composed of the cladding layer 257, the core portion 256, and the cladding layer 255 are cut by the dicing blade to form the inclined surfaces 251A, 251B. Then, the mirrors 253, 254 are formed by forming a metal film on the inclined surfaces 251A, 251B, and then the supporting substrate is removed. Thus, the optical waveguide 202 is formed.
Then, in steps shown in FIG. 6, the optical waveguide 202 is bonded onto the solder resist 226 of the wiring substrate 201. Then, in steps shown in FIG. 7, the light emitting element 203 and the light receiving element 204 are mounted on the wiring substrate 201, and then the underfill resins 206, 207 are formed. Thus, the optical/electrical hybrid substrate 200 is manufactured (see JP-A-2001-281479, for example).
However, in the optical/electrical hybrid substrate 200 in the related art, the terminal 261 of the light emitting element 203 and the terminal 266 of the light receiving element 204 are connected to the pad portions 241, 242 of the wiring substrate 201 manufactured separately from the optical waveguide 202, respectively. Therefore, it was difficult to position the optical waveguide 202, the light emitting element 203, and the light receiving element 204 on the wiring substrate 201 with good precision such that the distance R1 from the center position S1 (the center position on the optical axis) of the mirror 253 to the center position of the pad portion 241, the distance N1 from the light emitting portion 262 to the center position S1 (the center position on the optical axis) of the mirror 253, the distance R2 from the center position S2 (the center position on the optical axis) of the mirror 254 to the center position of the pad portion 242, and the distance N2 from the light receiving portion 267 to the center position S2 (the center position on the optical axis) of the mirror 254 coincide with the given distances RA, NA, RB, NB respectively.
As a result, such a problem existed that a transmission loss of the light signal between the light emitting element 203 and the optical waveguide 202 and a transmission loss of the light signal between the light receiving element 204 and the optical waveguide 202 are increased.